docs: def download(directory, youtube_id, clear=False):
      """Download the audio of a YouTube video.
  
      The audio is downloaded in the highest available quality. Progress is
      printed to `stdout`. The file is named `youtube_id.m4a`, where
      `youtube_id` is the 11-character code identifiying the YouTube video
      (can be determined from the URL).
  
      Parameters
      ----------
      directory : str
          The directory in which to save the downloaded audio file.
      youtube_id : str
          11-character video ID (taken from YouTube URL)
      clear : bool
          If `True`, it deletes the downloaded video. Otherwise it downloads
          it. Defaults to `False`.
  
      """
      filepath = os.path.join(directory, '{}.m4a'.format(youtube_id))
      if clear:
          os.remove(filepath)
          return
      if not PAFY_AVAILABLE:
          raise ImportError("pafy is required to download YouTube videos")
      url = 'https://www.youtube.com/watch?v={}'.format(youtube_id)
      video = pafy.new(url)
      audio = video.getbestaudio()
      audio.download(quiet=False, filepath=filepath)